What broad emission lines tell us about how active galactic nuclei work

By M. Gaskell. 2009

183 citations recorded by the source corpus.

I review progress made in understanding the nature of the broad-line region (BLR) of active galactic nuclei (AGNs) and the role BLRs play in the AGN phenomenon. The high equivalent widths of the lines imply a high BLR covering factor, and the absence of clear evidence for absorption by the BLR means that the BLR has a flattened distribution and that we always view it near pole-on. The BLR gas is strongly self-shielding near the equatorial plane. Velocity-resolved reverberation mapping has long strongly excluded significant outflow of the BLR and shows instead that the predominant motions are Keplerian with large turbulence and a significant net inflow. The rotation and turbulence are consistent with the inferred geometry. The blueshifting of high-ionization lines is a consequence of scattering off inflowing material rather than the result of an outflowing wind. The rate of inflow of the BLR is sufficient to provide the accretion rate needed to power the AGN. Because the motions of the BLR are gravitationally dominated, and the BLR structure is very similar in most AGNs, consistent black hole masses can be determined. The good correlation between these estimates and masses predicted from the bulge luminosities of host galaxies provides strong support for the similarity of AGN continuum shapes and the correctness of the BLR picture presented. It is concluded that although many mysteries remain about the details of how AGNs work, a general overall picture of the torus and BLR is becoming clear.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/1c976b1bf6d9daf164c5108707f6eef6ee3b5669

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Citations in the corpus

PS1-10jh: THE DISRUPTION OF A MAIN-SEQUENCE STAR OF NEAR-SOLAR COMPOSITION (2013, background): “However, all thermal AGN show an excess in the blue known as the “big blue bump” (Shields 1978; Lawrence 2012), and the slopes of their continuum Fν ∝ ν−1 (Gaskell 2009).”
An expanded Mbh–σ diagram, and a new calibration of active galactic nuclei masses (2010, background): “…width V of the emission lines from the clouds, and assuming that their motion is virialized and dominated by the central black hole’s gravity (e.g. Gaskell 1988, 2009a; Koratkar & Gaskell 1991; Wandel, Peterson & Malkan 1999; Onken & Peterson 2002), one can compute the virial product VP = r V2/G.”
UNIFICATION OF LUMINOUS TYPE 1 QUASARS THROUGH C iv EMISSION (2010, background): “We note that Gaskell (2009) has recently commented that outflows are “ruled out” by early reverberation mapping results.”
The origin of the broad line region in active galactic nuclei (2010, background): “Done & Krolik 1996, Elvis 2000, Ferland et al. 2009, Gaskell 2009; Shapovalova et al. 2010).”
Determining Inclinations of Active Galactic Nuclei Via Their Narrow-Line Region Kinematics (2012, result): “If the BLR kinematics contain a strong rotational component, as suggested by a number of studies (Murray & Chiang 1997; Gaskell 2000, 2009), this correlation suggests that pole-on and near pole-on AGN contain velocities that may be underestimated.”